The marked change in the density of stars visible on either side indicates that the strip of glowing hydrogen marks the edge of a substantial dark cloud. As a cloud core emerging from its parental cloud, and as an active site of low-mass star formation.
Small red spots in the base of the Horsehead betray the presence of hidden proto-stars, and red streaks near the yellowish nebula surrounding V615 Orionis (bottom left) are Herbig-Haro objects, which are jets of material ejected from protostars. The Horsehead is a fascinating, active, and complex neighborhood.
Location: 05 38 27 -02 29 (1950.0), constellation of Orion.
Distance: about 1600 light-years.
Image Credit: N.A.Sharp/NOAO/AURA/NSF